Retroreflective articles including a security mark

ABSTRACT

The present disclosure relates to prismatic retroreflective articles that includes a security mark and to methods of making such articles.

BACKGROUND

Retroreflective materials are characterized by the ability to redirectlight incident on the material back toward the originating light source.This property has led to the widespread use of retroreflective sheetingfor a variety of traffic and personal safety uses. Retroreflectivesheeting is commonly employed in a variety of articles, for example,road signs, barricades, license plates, pavement markers and markingtape, as well as retroreflective tapes for vehicles and clothing.

Two known types of retroreflective sheeting are optical element sheeting(e.g., cube corner sheeting) and microsphere-based sheeting.Microsphere-based sheeting, sometimes referred to as “beaded” sheeting,employs a multitude of microspheres typically at least partiallyembedded in a binder layer and having associated specular or diffusereflecting materials (e.g., pigment particles, metal flakes or vaporcoats, etc.) to retroreflect incident light. Cube corner retroreflectivesheeting, sometimes referred to as “prismatic” sheeting, typicallycomprises a thin transparent layer having a substantially planar firstsurface and a second structured surface comprising a plurality ofgeometric structures, some or all of which include three reflectivefaces configured as a cube corner element.

A cube corner element can include three mutually perpendicular opticalfaces that intersect at a single apex. Generally, light that is incidenton a corner cube element from a light source is totally internallyreflected from each of the three perpendicular cube corner optical facesand is redirected back toward the light source. Presence of, forexample, dirt, water, and adhesive on the optical faces can preventtotal internal reflection (TIR) and lead to a reduction in theretroreflected light intensity.

Security marks are used to indicate that an article is authentic.Security marks have been used on beaded retroreflective sheeting. Forexample, U.S. Pat. No. 4,688,894 describes a security mark for use onbeaded retroreflective sheeting having the ability to be opticallyvariable based on viewing angle. U.S. Pat. No. 7,995,278 describes asecurity mark for use on beaded retroreflective sheeting that appears tofloat or sink along the article sheeting surface.

BRIEF SUMMARY

The inventors of the present application recognized a need for securitymarks capable of use on prismatic retroreflective sheeting. The presentdisclosure relates to prismatic retroreflective articles that includes asecurity mark and to methods of making such articles.

In one illustrative embodiment, a retroreflective article includes aretroreflective layer including multiple cube corner elements thatcollectively form a structured surface; one or more barrier layerspositioned adjacent to the structured surface; and a conforming layerpositioned adjacent to the one or more barrier layers; wherein one ormore of the layers in combination form a security mark having a firstportion including a first characteristic and a second portion includinga second characteristic, wherein the characteristic is one of color andinfra-red absorbency. For purposes of clarity, the one or more barrierlayers have a characteristic that varies from a characteristic in one of(1) the areas not including the one or more barrier layers or (2)another barrier layer. Exemplary characteristics include, for example,color and infrared absorbency.

In some embodiments, at least some of the first and second portionsoverlap. In some embodiments, the first and second portions do notoverlap. In some embodiments, the barrier layers are applied to theconforming layer. In some embodiments, the barrier layers are applied toat least a portion of the structured surface. In some embodiments, theone or more barrier layers cover less than 100% of the structuredsurface. In some embodiments, the structured surface that is adjacent tothe one or more barrier layers is optically active and the portion ofthe structured surface not adjacent to the one or more barrier layers isnot optically active. In some embodiments, the conforming layer is anadhesive. In some embodiments, the adhesive is optically opaque. In someembodiments, the security mark can be distinguished from the backgroundby a viewer in both ambient light and in retroreflection. In someembodiments, the security mark can be distinguished from the backgroundby a viewer in ambient light, but not in retroreflection.

In another illustrative embodiment, a method of forming aretroreflective article includes providing a retroreflective layerincluding multiple cube corner elements that collectively form astructured surface; positioning one or more barrier layers adjacent tothe structured surface to form a security mark having a first portionincluding a first characteristic and a second portion including a secondcharacteristic, wherein the characteristic is one of color and infra-redabsorbency; positioning a conforming layer adjacent to the one or morebarrier layers; and laminating the layers.

In some embodiments, the method further includes forming a pattern ofthe one or more barrier layers on the conforming layer before thelaminating step. In some embodiments, the method further includesforming a pattern on one or more of the barrier layers before thelaminating step. In some embodiments, the method further includespatterning the one or more barrier layers onto the conforming layerbefore the laminating step to form a security mark void; and patterninganother barrier layer into the security mark void, wherein the barrierlayer and the security mark do not substantially overlap. In someembodiments, the one or more barrier layers are formed by curing apolymer-containing layer before the laminating step. In someembodiments, the one or more barrier layers are printed onto theconforming layer. In some embodiments, the laminating step encapsulatesair between the structured surface and the one or more barrier layers.In some embodiments, the security mark can be distinguished from thebackground by a viewer in both ambient light and in retroreflection. Insome embodiment, the security mark can be distinguished from thebackground by a viewer in ambient light, but not in retroreflection. Insome embodiments, the confirming layer is an adhesive. In someembodiments, the adhesive is a pressure sensitive adhesive. In someembodiments, the adhesive is optically opaque. In some embodiments, thesecurity mark exhibits variable retroreflectivity.

These and various other features and advantages will be apparent from areading of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in view of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIGS. 1A and 1B are schematic side views of one exemplary embodiment ofa retroreflective article.

FIG. 2 is schematic drawing of one exemplary intermediary step that canbe used in forming a retroreflective article.

FIG. 3 is schematic drawing of one exemplary intermediary step that canbe used in forming a retroreflective article.

FIG. 4 is a photograph from a front view of an illustrativeretroreflective article with security markings.

FIG. 5 is a schematic side view of another exemplary embodiment of aretroreflective article.

FIG. 6 is a schematic side view of another exemplary embodiment of aretroreflective article.

The figures are not to scale. Like numbers used in the figures refer tolike components. However, it will be understood that the use of a numberto refer to a component in a given figure is not intended to limit thecomponent in another figure labeled with the same number.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying setof drawings that form a part hereof and in which are shown by way ofillustration several specific embodiments. It is to be understood thatother embodiments are contemplated and may be made without departingfrom the scope or spirit of the present disclosure. The followingdetailed description, therefore, is not to be taken in a limiting sense.

The present disclosure relates to prismatic retroreflective articlesthat includes a security mark and to methods of making such articles.The term “security mark” refers to an element on or in a retroreflectivefilm that can be used to authenticate the article. The security marks ofthe present application can be continuous or discontinuous.

FIGS. 1A and 1B are schematic side views of one exemplary embodiment ofa retroreflective article 100 that faces a viewer 102. Retroreflectivearticle 100 includes a retroreflective layer 110 including multiple cubecorner elements 112 that collectively form a structured surface 114opposite a major surface 116. The optical elements can be full cubes,truncated cubes, or preferred geometry (PG) cubes as described in, forexample, U.S. Pat. No. 7,422,334, incorporated herein by reference. Thespecific retroreflective layer 110 shown in FIGS. 1A and 1B includes anoverlay layer 118 (also referred to as a top film), but those of skillwill appreciate that some embodiments do not include an overlay layer.One or more barrier layers 134 are positioned between retroreflectivelayer 110 and conforming layer 132. Barrier layers 134 form a physical“barrier” between cube corner elements 112 and conforming layer 132.Barrier layer 134 can directly contact or be spaced apart from or canpush slightly into the tips of cube corner elements 112. Barrier layers134 have a characteristic that varies from a characteristic in one of(1) the areas not including barrier layers 134 or (2) another barrierlayer 134. Exemplary characteristics include, for example, color andinfrared absorbency.

In general, any material that prevents the conforming layer materialfrom contacting cube corner elements 112 or flowing or creeping into lowrefractive index area 138 can be used to form the barrier layerExemplary materials for use in barrier layer 134 include resins,polymeric materials, dyes, inks (including color-shifting inks), vinyl,inorganic materials, UV-curable polymers, multi-layer optical films(including, for example, color-shifting multi-layer optical films),pigments, particles, and beads. The size and spacing of the one or morebarrier layers can be varied. In some embodiments, the barrier layersmay form a pattern on the retroreflective sheeting. In some embodiments,one may wish to reduce the visibility of the pattern on the sheeting. Ingeneral, any desired pattern can be generated by combinations of thedescribed techniques, including, for example, indicia such as letters,words, alphanumerics, symbols, graphics, logos, or pictures. Thepatterns can also be continuous, discontinuous, monotonic, dotted,serpentine, any smoothly varying function, stripes, varying in themachine direction, the transverse direction, or both; the pattern canform an image, logo, or text, and the pattern can include patternedcoatings and/or perforations. The pattern can include, for example, anirregular pattern, a regular pattern, a grid, words, graphics, imageslines, and intersecting zones that form cells.

A low refractive index area 138 is positioned between (1) one or both ofbarrier layer 134 and conforming layer 132 and (2) cube corner elements112. The low refractive index area 138 facilitates total internalreflection such that light that is incident on cube corner elements 112adjacent to a low refractive index area 138 is retroreflected. As isshown in FIG. 1B, a light ray 150 incident on a cube corner element 112that is adjacent to low refractive index layer 138 is retroreflectedback to viewer 102. For this reason, an area of retroreflective article100 that includes low refractive index layer 138 can be referred to asan optically active area. In contrast, an area of retroreflectivearticle 100 that does not include low refractive index layer 138 can bereferred to as an optically inactive area because it does notsubstantially retroreflect incident light. As used herein, the term“optically inactive area” refers to an area that is at least 50% lessoptically active (e.g., retroreflective) than an optically active area.In some embodiments, the optically inactive area is at least 40% lessoptically active, or at least 30% less optically active, or at least 20%less optically active, or at least 10% less optically active, or atleast at least 5% less optically active than an optically active area.

Low refractive index layer 138 includes a material that has a refractiveindex that is less than about 1.30, less than about 1.25, less thanabout 1.2, less than about 1.15, less than about 1.10, or less thanabout 1.05. In general, any material that prevents the conforming layermaterial from contacting cube corner elements 112 or flowing or creepinginto low refractive index area 138 can be used as the low refractiveindex material. In some embodiments, barrier layer 134 has sufficientstructural integrity to prevent conforming layer 132 from flowing into alow refractive index area 138. In such embodiments, low refractive indexarea may include, for example, a gas (e.g., air, nitrogen, argon, andthe like). In other embodiments, low refractive index area includes asolid or liquid substance that can flow into or be pressed into or ontocube corner elements 112. Exemplary materials include, for example,ultra-low index coatings (those described in PCT Patent Application No.PCT/US2010/031290), and gels.

The portions of conforming layer 132 that are adjacent to or in contactwith cube corner elements 112 form non-optically active (e.g.,non-retroreflective) areas or cells. In some embodiments, conforminglayer 132 is optically opaque. In some embodiments conforming layer 132has a white color.

In some embodiments, conforming layer 132 is an adhesive. Exemplaryadhesives include those described in PCT Patent Application No.PCT/US2010/031290. Where the conforming layer is an adhesive, theconforming layer may assist in holding the entire retroreflectiveconstruction together and/or the viscoelastic nature of barrier layers134 may prevent wetting of cube tips or surfaces either initially duringfabrication of the retroreflective article or over time.

In some embodiments, conforming layer 132 is a pressure sensitiveadhesive. The PSTC (pressure sensitive tape council) definition of apressure sensitive adhesive is an adhesive that is permanently tacky atroom temperature which adheres to a variety of surfaces with lightpressure (finger pressure) with no phase change (liquid to solid). Whilemost adhesives (e.g., hot melt adhesives) require both heat and pressureto conform, pressure sensitive adhesives typically only require pressureto conform. Exemplary pressure sensitive adhesives include thosedescribed in U.S. Pat. No. 6,677,030. Barrier layers 134 may alsoprevent the pressure sensitive adhesive from wetting out the cube cornersheeting.

In some embodiments, conforming layer 132 includes a sealing film 136that assists in holding the construction together. Some sealing filmsrequire heat and pressure to conform.

In one exemplary embodiment, one or more barrier layers are printed in afirst region (e.g., a background region) with one (or more) firstcolors, and one or more barrier layers are printed in a second region(e.g., a security mark region) with one or more second colors. The firstand second regions combine to create a security mark. In thisembodiment, the security mark is defined by the color differentialbetween the first region and the second region.

In some exemplary embodiments, the security mark is visible in ambientlight (the visible spectrum) and “disappears” in retroreflection. Thiscould be done, for example, by making a security mark with colored areasthat have the same size, shape, and/or spacing as the background but atleast one color that is different from the background color. In ambientlight, the different colors make the mark apparent. However, because thecolor of the areas including barrier material(s) does not affect theappearance of the film in retroreflected light, the mark lookseffectively the same as the background.

In some embodiments, the security mark is visible in retroreflection andis not substantially visible in ambient light. This could be done, forexample, by creating an image area having a higher percentage coverageof conforming material than adjacent areas, and in the same image area,using a pigment to adjust the conforming layer to have a lower cap-Y(i.e., grayer appearance) than the adjacent conforming material. Theresult is that both areas appear the same color in diffuse light. Theimage area appears less reflective in retroreflection. Alternatively,this could be done by, for example, using barriers layers havingdissimilar colors that do not have a high degree of contrast between thecolors.

Retroreflective layer 110 of FIGS. 1A and 1B is shown as includingoverlay layer 118 and no land layer or land portion. The term “landlayer” as used in the present application refers to a continuous layerof material coextensive with the cube corner elements and composed ofthe same material. Those of skill in the art will appreciate thatretroreflective layer 110 can include a land layer or land portion. Aconstruction without a land layer may be desirable for flexibleembodiments.

In some embodiments, one or more barrier layers are printed on a filmthat is later positioned adjacent to the structured surface of theretroreflective layer.

One implementation of these embodiments is schematically shown in FIG.2. FIG. 2 shows one method of making at least some of theretroreflective articles of the present disclosure involves placingbarrier layer material 134 onto a pressure sensitive adhesive material132 and then laminating the resulting pressure sensitive adhesive layer130 to a retroreflective layer 110. The pressure sensitive adhesivelayer 130 can be formed in a variety of ways including but not limitedto the following exemplary methods. In one exemplary embodiment, thematerial(s) forming the barrier layer are printed onto the pressuresensitive adhesive. The method of printing can be, a non-contact methodsuch as, for example, printing using an inkjet printer. The method ofprinting can be a contact printing method such as, for example,flexographic printing. In another exemplary embodiment, the material(s)forming the barrier layer are printed onto a flat release surface using,for example, an inkjet or screen printing method, and are thensubsequently transferred from the flat release surface onto the pressuresensitive adhesive. In another exemplary embodiment, the material(s)forming the barrier layer are flood coated onto a microstructuredsurface. The barrier layer material is subsequently transferred from themicrostructured surface to the pressure sensitive adhesive by, forexample, lamination. The structured surface is removed after laminationto provide a pressure sensitive adhesive with barrier layers that islaminated to a retroreflective layer to make the retroreflectivearticle. The retroreflective article may then, optionally, be adhesivelybonded to a substrate (e.g., an aluminum substrate) to form, forexample, a license plate or signage.

In some embodiments, one or more barrier layers are applied (e.g.,printed) on the cube corner elements and a film layer is later placed ontop of the barrier layers and cube corner elements. One implementationof these embodiments is schematically shown in FIG. 3.

FIG. 4 is a front view of an illustrative retroreflective article 100with two separate security markings 134. The retroreflective article 100shown has a white, opaque, retroreflective background and black or graysecurity markings 134. Under ambient light, the security markings 134appear black or gray and under retroreflection the security markings 134appear brighter than the surrounding background.

FIGS. 5 and 6 are a schematic side view of another exemplary embodimentof a retroreflective article 101. This embodiment is similar to FIGS. 1Aand 1B except that multiple barrier layers 134 and 135 are shown. Thebarrier layers in FIG. 5 are overlapping, and the barrier layers in FIG.6 are not substantially overlapping. Those of skill in the art willappreciate that in some embodiments, the barrier layers partiallyoverlap.

With specific reference to the embodiment shown in FIG. 5, the differentbarrier layers 134 and 135 can have the same or similar physicalproperties or can have different physical properties. In someembodiments, barrier layers 134 and 135 do not have the same color. Insome embodiments, barrier layer 134 is clear or colorless while barrierlayer 135 has a color and/or is opaque. In some embodiments, barrierlayer 134 and conforming layer 132 have the same color (e.g., white).Barrier layer 135 can have a color that is different than either or bothof pressure sensitive adhesive layer 132 and barrier layer 134.

With specific reference to the embodiment shown in FIG. 6, this securitymarking can be formed by, for example, first patterning (e.g., printing)barrier layer 134 onto the conforming layer 132 where the barrier layer135 defines a security mark void and then patterning barrier layer 135into the security mark void. Thus, barrier layer 134 and barrier layer135 are not overlapping.

In some embodiments, the security mark changes appearance to a viewer asthe viewer changes their point of view. For example, as the observationangle and/or entrance angle changes, the appearance of the security markchanges.

In some embodiments, the conforming layer conforms less than completelyin the optically inactive areas. The optical effect of this is that theoptically inactive areas may be partially or somewhat optically active(e.g., retroreflective). In other words, the retroreflectivity or lackthereof can be varied in both the optically inactive and opticallyactive areas. The conformance of the conforming layer can be modified tocreate this optical effect.

Some embodiments of the security marks described in the presentapplication do not interfere with reading of the license platecharacters. This means that the security mark does not interfere withreading of the license plate alphanumerics in at least one lightspectrum, e.g., visible, infra-red, retroreflection. In someembodiments, the security feature(s) on a license plates can be read byoptical character recognition cameras without confusion between thealphanumeric characters that form the license plate number and thesecurity marks.

Some embodiments of the security marks described in the presentapplication increase or decrease the retroreflectivity of certain areasof the security mark relative to the background area. By comparison,prior art security marks on beaded sheeting could only decrease theretroreflectivity. Increasing or decreasing the retroreflectivity ofcertain areas of the security mark can be done, for example, by varyingthe dimensions and/or percent optically active area of repeating unitsin a pattern of barrier layers.

Some embodiments of the security marks described in the presentapplication increase or decrease the whiteness or CAP-Y of certain areasof the security mark relative to the background area. Increasing ordecreasing the whiteness or CAP-Y of certain areas of the security markcan be done, for example, by varying the dimensions and/or percentoptically active area of repeating units in a pattern of barrier layers.Alternatively or additionally, the barrier material can be white, whichcould, in some embodiments, increase the CAP-Y of the security mark incomparison with the background area.

All references mentioned herein are incorporated by reference.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

Spatially related terms, including but not limited to, “lower,” “upper,”“beneath,” “below,” “above,” and “on top,” if used herein, are utilizedfor ease of description to describe spatial relationships of anelement(s) to another. Such spatially related terms encompass differentorientations of the device in use or operation in addition to theparticular orientations depicted in the figures and described herein.For example, if a cell depicted in the figures is turned over or flippedover, portions previously described as below or beneath other elementswould then be above those other elements.

Embodiments of the present disclosure are disclosed. The disclosedembodiments are presented for purposes of illustration and notlimitation. The implementations described above and otherimplementations are within the scope of the following claims. Oneskilled in the art will appreciate that the present disclosure can bepracticed with embodiments other than those disclosed. Those havingskill in the art will appreciate that many changes may be made to thedetails of the above-described embodiments and implementations withoutdeparting from the underlying principles thereof. Further, variousmodifications and alterations of the present invention will becomeapparent to those skilled in the art without departing from the spiritand scope of the present disclosure. The scope of the presentapplication should, therefore, be determined only by the followingclaims.

What is claimed is:
 1. A retroreflective article, comprising: aretroreflective layer including multiple cube corner elements thatcollectively form a structured surface; one or more barrier layerspositioned adjacent to the structured surface creating low refractiveindex areas between the barrier layers and the structured surface havinga lower index of refraction than the retroreflective layer; and aconforming adhesive layer positioned adjacent to the one or more barrierlayers, wherein the conforming layer is optically opaque; wherein one ormore of the layers in combination form a security mark having a firstportion including a first characteristic and a second portion includinga second characteristic different from the first characteristic, whereinthe characteristic is one of color and infra-red absorbency; wherein thefirst and second portions do not overlap, and wherein the conformingadhesive layer further comprises a portion of the security mark byadjusting a color of the conforming layer material forming such portionto have a grayer appearance than adjacent conforming layer material suchthat the portion and adjacent conforming layer material appear the samecolor in diffuse light.
 2. The retroreflective article of claim 1,wherein at least some of the first and second portions overlap forming acontiguous multiple different color barrier layer, and wherein thesecurity mark is defined by a color differential between the first andsecond portions of the contiguous barrier layer.
 3. The retroreflectivearticle of claim 1, wherein one or more of the barrier layers areapplied to the conforming layer wherein such one or more barrier layershave dissimilar colors that do not have a high degree of contrastbetween the dissimilar colors.
 4. The retroreflective article of claim1, wherein one or more of the barrier layers are applied to at least aportion of the structured surface and wherein the security mark isvisible in retroreflection and not as visible in ambient light.
 5. Theretroreflective article of claim 1, wherein the one or more barrierlayers cover less than 100% of the structured surface.
 6. Theretroreflective article of claim 1, wherein the portion of thestructured surface adjacent to the one or more barrier layers isoptically active and the portion of the structured surface not adjacentto the one or more barrier layers is not optically active.
 7. Theretroreflective article of claim 1, wherein the conforming layer is anadhesive.
 8. The retroreflective article of claim 1, wherein thesecurity mark can be distinguished from a background by a viewer in bothambient light and in retroreflection.
 9. The retroreflective article ofclaim 1, wherein the security mark can be distinguished from abackground by a viewer in ambient light, but not in retroreflection. 10.The retroreflective article of claim 1, wherein the one or more barrierlayers have a characteristic that varies from a characteristic in one of(1) the areas not including the one or more barrier layers or (2)another barrier layer.
 11. A method of forming a retroreflectivearticle, comprising: providing a retroreflective layer includingmultiple cube corner elements that collectively form a structuredsurface; positioning one or more barrier layers adjacent to thestructured surface to form a security mark having a first portionincluding a first characteristic and a second portion including a secondcharacteristic different from the first characteristic, wherein thecharacteristic is one of color and infra-red absorbency creating lowrefractive index areas between the barrier layers and the structuredsurface having a lower index of refraction than the retroreflectivelayer; positioning a conforming adhesive layer adjacent to the one ormore barrier layers, wherein the conforming layer is optically opaque;and laminating the layers; wherein the first and second portions do notoverlap, and wherein the conforming adhesive layer further comprises aportion of the security mark by adjusting a color of the conforminglayer material forming such portion to have a grayer appearance thanadjacent conforming layer material such that the portion and adjacentconforming layer material appear the same color in diffuse light. 12.The method of claim 11, further comprising: forming a pattern of the oneor more barrier layers on the conforming layer before the laminatingstep such that the security mark is visible in retroreflection and notas visible in ambient light.
 13. The method of claim 11, furthercomprising: forming a pattern on one or more of the barrier layersbefore the laminating step.
 14. The method of claim 11, furthercomprising: patterning the one or more barrier layers onto theconforming layer before the laminating step to form a security markvoid; and patterning another barrier layer into the security mark void,wherein the another barrier layer and the security mark do notsubstantially overlap.
 15. The method of claim 11, wherein the one ormore barrier layers is formed by curing a polymer-containing layerbefore the laminating step.
 16. The method of claim 11, wherein the oneor more barrier layers is printed onto the conforming layer.
 17. Themethod of claim 11, wherein the laminating step encapsulates air betweenthe structured surface and the one or more barrier layers.
 18. Themethod of claim 11, wherein the security mark can be distinguished fromthe background by a viewer in both ambient light and in retroreflection.19. The method of claim 11, wherein the security mark can bedistinguished from the background by a viewer in ambient light, but notin retroreflection.
 20. The method of claim 11, wherein the adhesive isa pressure sensitive adhesive.
 21. The method of claim 11, wherein thesecurity mark exhibits variable retroreflectivity.
 22. The method ofclaim 11, wherein the one or more barrier layers have a characteristicthat varies from a characteristic in one of (1) the areas not includingthe one or more barrier layers or (2) another barrier layer.